Mesophase pitch for carbon fiber production using supercritical carbon dioxide

ABSTRACT

Embodiments of methods for improving mesophase pitch for carbon fiber production using supercritical carbon dioxide are described. The methods improve the relative amount and quality of mesophase pitch in feedstocks, such as coal tar, already having at least some mesophase pitch. One particular method includes performing a sCO2/toluene extraction on the coal tar to obtain a toluene insoluble fraction of the coal tar; mixing the toluene insoluble fraction with sCO2 to obtain a sCO2/toluene insoluble fraction mixture; and extruding the sCO2/toluene insoluble fraction mixture, thereby separating the sCO2 from the toluene insoluble fraction to obtain fibers of mesophase pitch.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of U.S. Provisional PatentApplication Nos. 62/820,162, titled “Improving Mesophase Pitch forCarbon Fiber Production Using Supercritical Carbon Dioxide” and filedMar. 18, 2019 which application is hereby incorporated by referenceherein.

INTRODUCTION

Pyrolysis refers to a thermochemical decomposition of organic materialat elevated temperatures in the absence of oxygen. Depending on how apyrolysis system is configured and operated, different pyrolysisproducts can be obtained. There are systems and methods for generatingcoal tar via the pyrolysis of coal using supercritical carbon dioxide.In some of those systems and methods, the resulting coal tar productincludes at least some mesophase material which can be used to createmesophase pitch. Mesophase pitch refers to an anisotropic liquidcrystalline phase of pitch characterized by pre-graphitic order, highdensity, and high softening temperature. Mesophase pitch can be used tomake high performance carbon fiber.

Improving Mesophase Pitch for Carbon Fiber Production UsingSupercritical Carbon Dioxide

Embodiments of methods for improving mesophase pitch for carbon fiberproduction using supercritical carbon dioxide are described. The methodsimprove the relative amount and quality of mesophase pitch infeedstocks, such as coal tar, already having at least some mesophasepitch. One particular method includes performing a sCO2/tolueneextraction on the coal tar to obtain a toluene insoluble fraction of thecoal tar; mixing the toluene insoluble fraction with sCO2 to obtain asCO2/toluene insoluble fraction mixture; and extruding the sCO2/tolueneinsoluble fraction mixture, thereby separating the sCO2 from the tolueneinsoluble fraction to obtain fibers of mesophase pitch.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawing figures, which form a part of this application,are illustrative of described technology and are not meant to limit thescope of the invention as claimed in any manner, which scope shall bebased on the claims appended hereto.

FIG. 1 illustrates, at a high-level, a simplified embodiment of apyrolysis method that improves the relative amount of pitch producedfrom a given feedstock.

FIG. 2 illustrates a more detailed embodiment of the pyrolysis method ofFIG. 1.

FIG. 3 is an example of a system suitable for the pitch productionmethods described above.

FIG. 4 illustrates a process flow diagram for a batch embodiment offlexible pyrolysis system that can be tuned to change the pyrolysisproducts obtained from a given feedstock.

FIGS. 5A-5C illustrate the experimental performance of an embodiment ofthe system shown in FIG. 4.

FIG. 6 illustrates an embodiment of a broad method for pyrolyzingcarbonaceous feedstock to obtain reaction products using CO₂.

FIG. 7 is a more detailed embodiment of a method for pyrolyzing coalwith supercritical CO₂.

FIG. 8 illustrates an embodiment of a method for improving mesophasepitch for carbon fiber production using supercritical carbon dioxide.

DETAILED DESCRIPTION

Before the systems and methods for preparing improved mesophase pitchfor carbon fiber production using supercritical carbon dioxide aredisclosed and described, it is to be understood that this disclosure isnot limited to the particular structures, process steps, or materialsdisclosed herein, but is extended to equivalents thereof as would berecognized by those ordinarily skilled in the relevant arts. It shouldalso be understood that terminology employed herein is used for thepurpose of describing particular embodiments only and is not intended tobe limiting. It must be noted that, as used in this specification, thesingular forms “a,” “an,” and “the” include plural referents unless thecontext clearly dictates otherwise. Thus, for example, reference to “alithium hydroxide” is not to be taken as quantitatively or sourcelimiting, reference to “a step” may include multiple steps, reference to“producing” or “products” of a reaction should not be taken to be all ofthe products of a reaction, and reference to “reacting” may includereference to one or more of such reaction steps. As such, the step ofreacting can include multiple or repeated reaction of similar materialsto produce identified reaction products.

Pitch refers to a collection of hydrocarbons including polyaromatichydrocarbons that can be manufactured from coal, wood and other organicmaterial. Pitch is characterized by having high (>80% by weight)elemental carbon composition, high concentration of polycyclic aromatichydrocarbons (PAHs), and a softening temperature, where the softeningtemperature can range from 100° C. to greater than 250° C. (measuredusing the Vicat method ASTM-D 1525). Generally, pitch suitable forcarbon fiber will be capable of forming a high concentration ofanisotropic mesophase pitch. It can be used as a base for coatings andpaint, in roofing and paving, and as a binder in asphalt products. Pitchmay also be used to create carbon fiber as discussed in greater detailbelow.

While the systems and methods below will be presented in terms of asupercritical carbon dioxide embodiment, any supercritical fluid may beused such as carbon dioxide, water, methane, nitrous oxide, ethane,propane, ethylene, propylene, methanol, ethanol, acetone, etc. ormixtures of supercritical fluids.

FIG. 1 illustrates, at a high-level, a simplified embodiment of apyrolysis method that improves the relative amount of pitch producedfrom a given feedstock. In the method 100 shown, a carbonaceousfeedstock material and water are subjected to a two-stage pyrolysis. Thewater may exist as moisture content within the feedstock. Alternatively,additional water may be added to the feedstock at some point before orduring the pyrolysis.

The first stage is a low temperature pyrolysis operation 102 to removeC₁-C₄ gases from the feedstock. In this stage 102, the pyrolysis isperformed at a lower temperature (e.g., 150-350° C. at from 7-30 MPa).The feedstock are heated to the first stage temperature and held at thattemperature to generate and remove C₁-C₄ gases from the feedstock. In anembodiment, the gases in the pyrolysis reaction chamber are monitoredand, when it is determined that the C₁-C₄ gas concentration has begun tolevel off based on the operator's criteria, a higher temperaturepyrolysis operation 104 is performed.

The first stage temperature may be selected based on prior knowledge ofthe properties of the feedstock or may be automatically determined basedon a real-time analysis of the pyrolysis reaction and the products beinggenerated. Depending on the embodiment, the first stage temperature mayhave a lower range selected from 150° C., 175° C., 200° C., 225° C.,250° C., 275° C., 300° C. and 325° C. and may have an upper rangeselected from 175° C., 200° C., 225° C., 250° C., 275° C., 300° C., 325°C. and 350° C. so that any combination of the aforementioned lowerranges and upper ranges may be used.

In the second stage pyrolysis operation 104, the temperature isincreased to from 350-550° C. at from 7-30 MPa, for example from 7-12MPa, and held at that temperature for a period of time sufficient togenerate pitch. As with the first stage, the amount of pyrolysisreaction products generated will level off over time as the system comesto equilibrium and the length of the second pyrolysis operation 104 isat the operator's discretion.

The second stage temperature may be selected based on prior knowledge ofthe properties of the feedstock or may be automatically determined basedon a real-time analysis of the pyrolysis reaction and the products beinggenerated. Depending on the embodiment, the second stage temperature mayhave a lower range selected from 350° C., 375° C., 400° C., 425° C. 450°C., and 480° C. and may have an upper range selected from 375° C., 400°C., 425° C., 450° C., 450° C., 480° C., 500° C., 525° C., and 550° C. sothat any combination of the aforementioned lower ranges and upper rangesmay be used.

The pitch is then obtained in an extraction and separation operation106. In the extraction and separation operation 106 the pitch isextracted using a solvent, such as supercritical carbon dioxide (sCO₂),the solvent and dissolved pitch removed from the reaction chamber, andthen separated to produce a pitch product.

In order to obtain carbon fiber from the pitch, an optional (illustratedby dashed lines in the drawing) extrusion operation 108 may be performedin which the pitch is extruded into fibers of a desired cross-sectionalprofile and allowed to cool. The pitch may or may not be washed first,e.g., by toluene or other solvent, to remove unwanted products andrefine the pitch further.

Experimental data for two stage process of FIG. 1 indicates that thequantity of pitch produced for a given feedstock is greater than wouldotherwise be obtained from the same feedstock using a single stagepyrolysis at the higher temperature. Without being bound to anyparticular theory, the two stage process above appears to remove lighterhydrocarbons from the feedstock in the first stage, which makes themunavailable to react with the larger hydrocarbon chains and aromaticsduring the second stage and this improves the relative amount of pitchgenerated.

The feedstock material may include any carbonaceous material known inthe art. For example, the feedstock material may include, but is notlimited to, coal, biomass, mixed-source biomaterial, peat, tar, plastic,refuse, and landfill waste. For example, in the case of coal, thefeedstock may include, but is not limited to, bituminous coal,sub-bituminous coal, lignite, anthracite and the like. By way of anotherexample, in the case of biomass, the feedstock may include a woodmaterial, such as, but not limited to, softwoods or hardwoods. In thedetailed embodiments experiments discussed herein, the feedstock ispresented as coal. However, it will be understood that pitch may beequally generated from any other type of feedstock material and thensubsequently used to generate carbon fiber in the same manner asdescribed with coal.

It should be noted that any carbonaceous feedstock such as coal mayinclude some amount of water. In addition, water may be added to thefeedstock prior to or during pyrolysis in any of the methods and systemsdiscussed herein to modify the products created by the reaction.Likewise, feedstock may be dried prior to pyrolysis to lower the amountof water available during the pyrolysis operation and such a dryingoperation may be part of any of the methods and systems discussedherein.

FIG. 2 illustrates a more detailed embodiment of the pyrolysis method ofFIG. 1. The method 200 begins by placing the feedstock material andwater in a pyrolysis reaction chamber in a loading operation 202. In anembodiment, the feedstock material and/or the water may be pre-heatedbefore placement into the pyrolysis reaction chamber. The amount ofwater used may be from 1%-1000% the weight of the dried feedstockmaterial. In an embodiment, the amount of water may be from 10%, 20%,30%, 40%, or 50% the weight of dried feedstock material on the low endand up to 100%, 200%, or 500% on the high end. The water may be addedseparately or may already be in the feedstock material. For example, inan embodiment the feedstock material used is coal semi-saturated withwater such that more than 10% of the weight of the feedstock material iswater and the water in the coal is used as the water for the loadingoperation 202.

The loading operation may also include pressurizing the pyrolysisreaction chamber to the operating pressure (e.g., 7-12 MPa). In anembodiment, this may include removing oxygen and adding pressurized CO₂to the reaction chamber. In this embodiment, the pressurized CO₂ maylater be used as the solvent for extracting and removing the pitch andother soluble reaction products from the chamber.

The method 200 also includes heating pyrolysis reaction chamber to anintermediate temperature from 150 to 350° C. at from 7-12 MPa in aninitial heating operation 204. A narrower temperature range may be usedsuch as from 160, 170, 180, 190, 200, 210, 220, 230, or 240 at the lowerend of the range and to 250, 260, 270, 280, 290, 300, 310, 320, 330, or340 at the upper end of the range. The initial heating operation 204 maybe performed before or after the loading operation 202. In anembodiment, the operation 204 may be performed to increase thetemperature a fast as practicable with the given equipment so that thereactions at temperatures lower than the intermediate temperature arereduced.

The intermediate temperature is then maintained for a period of time ina first temperature hold operation 206. The hold time may be preselectedsuch as for 10, 15, 30, 60, 120 or even 240 minutes. For example, thepreselected hold time may be based on prior experiments. Alternatively,the hold time may be determined by monitoring the gases in the pyrolysisreaction chamber. For example, in an embodiment the concentration of oneor more pyrolysis reaction product gases such as methane, ethane,butane, propane, or any other light gas reaction product is monitored.The concentration of the monitored gas or gases will rise initially andultimately begin to level off roughly following an exponential curve.The hold time may be based on the monitored change in gas or gasesconcentration over time. For example, in an embodiment the firsttemperature hold operation 206 may be terminated when it is observedthat the concentration of monitored gas or gases has increased by lessthan some threshold amount (e.g., 2% or 100 ppm) over some predeterminedperiod (e.g., 10 seconds, 1 minute, 5 minutes, etc.). In yet anotherembodiment the amount of energy input into the chamber to maintain thepyrolysis temperature or any other parameter, such as visual or physicalcondition the feedstock material, may also be monitored to determinethat the reaction has progressed to the operator's satisfaction.

A second heating operation 208 is then performed. In the second heatingoperation 208, the temperature of the pyrolysis chamber and thefeedstock material is raised to a pyrolysis temperature from 300 to 550°C. For example, the second heating operation 208 may include heating thereaction chamber to from 325° C., 350° C., 375° C., or 400° C. on thelow end of the range to from 425° C., 450° C., 475° C., 500° C., 525°C., or 550° C. on the high end.

The pyrolysis temperature, which may also be referred to as the pitchproduction temperature, is then maintained for a second period of timefrom 1 minute to 24 hours in a second temperature hold operation 210.Again, the second hold time may be preselected, for example based onprior experiments. Alternatively, the hold time may be determined bymonitoring the one or more gases, which may or may be the same gas orgases monitored during the first temperature hold operation 206, in thepyrolysis reaction chamber. In yet another embodiment the amount ofenergy input into the chamber to maintain the pyrolysis temperature orany other parameter, such as visual or physical condition the feedstockmaterial, may also be monitored to determine that the reaction hasprogressed to the operator's satisfaction.

At the end of the second hold time, the pitch may be extracted andremoved from the pyrolysis chamber in an extraction operation 212.

A separation operation 214 may then be performed to separate theextracted pitch from the solvent. In an embodiment, if the solvent issCO₂ the separation operation 214 may include removing the sCO₂ anddissolved pyrolysis reaction products from the chamber from the chamberand reducing the temperature and pressure of the solvent until the pitchis obtained. For example, the sCO₂ may be passed through successivecollection chambers, each at a different pressure-temperaturecombination, in order to fractionally remove components of the reactionproducts, including the pitch, that have different solubilities incarbon dioxide. One of the separation chambers may be maintained at atemperature and pressure particular to the condensation of pitch fromthe solvent. For example, in an embodiment pitch is obtained from CO₂solvent in a chamber maintained at 350° C. or greater in temperature and7.39 MPa or greater in pressure.

In order to obtain carbon fiber from the pitch, an optional (illustratedby dashed lines in the drawing) extrusion operation 216 may be performedin which the pitch is extruded into fibers of a desired cross-sectionalprofile and allowed to cool. The pitch may or may not be washed first toremove unwanted products and refine the pitch further prior to or afterextrusion. Additionally, the extruded pitch may be drawn, dried, cooled,baked, heat-treated (in oxidative or inert environments), or otherwisepost-processed to improve the properties of the fiber strand.

The method 200 described above was described in terms of a batch processin a single pyrolysis reaction chamber. In an alternative embodiment themethod may be performed as a continuous or semi-continuous process usingone or more pyrolysis reaction chambers. For example, in an embodimentthe initial heating operation 204 and first temperature hold operation206 may be performed in a first reaction chamber and then the contentsmay be transferred to a second chamber for the second heating operation208 and second temperature hold operation 210.

FIG. 3 is an example of a system 300 suitable for the pitch productionmethods described above. FIG. 3 illustrates a block diagram view of asystem 300 for converting carbonaceous material to one or more reactionproducts. In one embodiment, the system 300 includes a thermochemicalconversion system 302. In one embodiment, the thermochemical conversionsystem 302 includes a thermochemical reaction chamber 304, such as apyrolysis reaction chamber, suitable for containing a volume offeedstock material and water 305 (e.g., carbonaceous material) andconverting the feedstock material to one or more reaction productsincluding pitch.

In the embodiment shown, the system 300 includes one or more heatsources 308 and a thermal energy transfer system 306 for transferringthermal energy from the one or more heat sources 308 to the volume offeedstock 305 contained within the thermochemical reaction chamber 304.The thermal energy transfer system 306 includes a heat transfer element307. For example, the heat transfer element 307 may include, but is notlimited to, a heat transfer loop, a heat transfer line and the like. Forinstance, the heat transfer element 307 may include, but is not limitedto, a heat transfer loop filled with a supercritical fluid (e.g., sCO₂)placed in thermal communication (e.g., directly or indirectly) with oneor more portions of the one or more heat sources 308.

In one embodiment, the thermal energy transfer system is arranged toselectably place the volume of the supercritical fluid in thermalcommunication with the volume of feedstock contained within thethermochemical reaction chamber. In this regard, the thermal energytransfer system 306 may selectably transfer thermal energy from the oneor more heat sources 308 to the volume of feedstock 305 contained withinthe at least one thermochemical reaction chamber 304. In anotherembodiment, the thermochemical reaction chamber 304 may pyrolyze least aportion of the feedstock 305 to obtain one or more reaction productsusing the thermal energy carried to the feedstock via the supercriticalfluid.

The supercritical fluid of system 300 may include any supercriticalfluid known in the art suitable for transferring energy from the one ormore heat sources 308 to the feedstock 305 contained in thethermochemical reaction chamber 304. In one embodiment, thesupercritical fluid includes, but is not limited to, sCO₂. In anotherembodiment, the supercritical fluid includes, but is not limited to,water, methanol, ethanol, propanol, acetone. In another embodiment, thesupercritical fluid is pressurized to high pressure within at least oneof the heat transfer element 307 and the thermochemical reaction chamber304.

It is noted herein that the supercritical fluid of system 300, such as,but not limited to CO₂, may have low viscosity and surface tension,allowing such supercritical fluids to readily penetrate organicmaterials (e.g., coal). The penetration of the supercritical fluid intothe feedstock 305 reduces the need for converting the feedstock 305 intofine particles prior to thermochemical reaction, thereby saving energyin the preparation of the feedstock material. In one embodiment, in casewhere the supercritical fluid is supercritical CO₂, the supercriticalfluid may be pressurized to above its critical pressure (7.39 MPa) andcritical temperature (31° C.). It is noted herein that above theseconditions, CO₂, will display unique solvency properties, similar toorganic solvents such as hexane, heptane, benzene, and toluene. Thenon-polar nature of supercritical CO₂ may facilitate the control ofundesirable ionic secondary reactions that commonly occur in aqueousenvironments. Further, CO₂ will volatize when the system isdepressurized below the critical conditions, which facilitates therecovery of oil with low content of water. Again, this may significantlyreduce energy consumption during reaction product-supercritical fluidseparation, described further herein, following pyrolysis. It is furthernoted herein that the supercritical fluid of system 300 applies heatedand pressurized CO₂ to the feedstock material 305, which provides forbetter control of reaction conditions (e.g., time, pressure, andtemperature), thereby allowing for better selectivity of high-valuetargeted chemical compounds or fuel intermediates.

In another embodiment, a supercritical fluid, such as supercritical CO₂,may provide strong temperature and reaction time control via theinjection of cooler supercritical fluid into the thermochemical reactionchamber 304 to quench the reaction or hotter supercritical fluid toaccelerate the reaction. It is further recognized that since a number ofsupercritical fluids, such as supercritical CO₂, can be efficientlycompressed, pressure conditions within the thermochemical reactionchamber 304 may also be used to control thermochemical reactions withinthe thermochemical reaction chamber 304.

In another embodiment, the solubility of one or more reaction products,such as pitch, in the supercritical fluid may be controlled by adding orremoving a polar material into the supercritical fluid. For example, thesolubility of one or more oils in supercritical carbon dioxide may becontrolled by the addition/removal of one or more materials including apolar molecule, such as, but not limited to, H₂O, ethanol, methanol,higher alcohols, and the like. By way of another example, in the casewhere the feedstock material includes coal, the solubility of one ormore oils in sCO₂ may be controlled by adding/removing one or morematerials including a hydrogen donor molecule, such as, but is notlimited to, H₂, H₂O, formic acid, tetralin, and any other hydrogen donorsolvents known in the art.

It is recognized herein that feedstock 305 contained within thethermochemical reaction chamber 304 may include sufficient moisture andpolar nature to adequately dissolve the one or more reaction products(e.g., bio-oil) in the supercritical fluid. As discussed further herein,the ‘ dryness’ of the feedstock may be controlled by the thermochemicalconversion system 302 (e.g., controlled via dryer 134), allowing thethermochemical conversion system 302 to maintain a moisture contentlevel within the feedstock 305 to a level sufficient for adequatelydissolving one or more reaction products in the supercritical fluid.

In another embodiment, the supercritical fluid may contain one or morematerials for enhancing one or more physical or thermochemical reactionsin the system 300. For example, the supercritical fluid may contain oneor more catalysts, such as, but not limited to, metals, metal salts andorganics. By way of another example, the supercritical fluid may containone or more solutes, such as, but not limited to, alcohols, oils,hydrogen and hydrocarbons.

The one or more heat sources 308 may include any heat source known inthe art suitable for providing thermal energy sufficient to heat thefeedstock 305 to the selected temperatures used in the two stages ofpyrolysis.

In one embodiment, the one or more heat sources 308 include a non-CO₂emitting heat source. In one embodiment, the one or more heat sources308 include one or more nuclear reactors. The one or more heat sources308 may include any nuclear reactor known in the art. For example, theone or more heat sources 308 may include a liquid metal cooled nuclearreactor, a molten salt cooled nuclear reactor, a high temperature watercooled nuclear reactor, a gas cooled nuclear reactor and the like. Byway of another example, the one or more heat sources 308 may include apool reactor. By way of another example, the one or more heat sources308 may include a modular reactor.

It is recognized herein that a nuclear reactor may generate temperaturessufficient to carry out pyrolysis (e.g., fast pyrolysis) of feedstock305. For example, a nuclear reactor heat source may generatetemperatures in excess of 350-600° C. In this regard, a nuclear reactormay be used to transfer thermal energy (e.g., at a temperature in excessof 350-600° C.) to the supercritical fluid. In turn, the supercriticalfluid may transfer the nuclear reactor generated thermal energy to thefeedstock 305 contained within the thermochemical reaction chamber 304.

It is further noted herein that a nuclear reactor heat source may beparticularly advantageous as a heat source in the context of system 300because the thermochemical reaction temperatures of system 300 arewithin the range of operating temperatures for many nuclear reactors.Nuclear reactor heat may be used to create reaction products (e.g.,pitch) in the thermochemical reaction chamber 304 at high efficiencysince the nuclear reactor is operating at the reaction temperature forthe thermochemical conversion (i.e., heat added at the thermochemicalreaction temperature supplies the required reaction enthalpy).

In one embodiment, as shown in FIG. 3, the thermal energy transfersystem 306 includes a direct heat exchange system configured to transferthermal energy directly from the one or more heat sources 308 to thevolume of the supercritical fluid of the heat transfer element 307. Forexample, the heat transfer element 307 may be placed in direct thermalcommunication with a portion of the one or more heat sources 308. Forinstance, in the case where the one or more heat sources 308 include anuclear reactor, one or more coolant systems of the nuclear reactor maybe integrated with the thermal energy transfer system 306. In thisregard, the nuclear reactor may utilize a supercritical fluid in one ormore coolant systems, which may then be coupled directly to thethermochemical reaction chamber 304. For example, a primary orintermediate coolant loop of the nuclear reactor may include a coolantfluid consisting of a supercritical fluid, such as supercritical CO₂.Further, the coolant loop of the nuclear reactor may be directly coupledto the thermochemical reaction chamber 304 via the thermal energytransfer system 306 so as to intermix the supercritical fluid of thecoolant loop of the nuclear reactor with the feedstock material 305contained within the thermochemical reaction chamber 304. In turn, upontransferring thermal energy from the nuclear reactor to the feedstockmaterial 305, the thermal energy transfer system 306 may circulate thesupercritical fluid coolant back to the nuclear reactor via return path318. It is further contemplated herein that the thermal energy transfersystem 306 may include any number of filtration elements in order toavoid transfer of feedstock and/or reaction products to the coolantsystem(s) of the nuclear reactor.

In another embodiment, not shown, the thermal energy transfer system 306includes an indirect heat exchange system. In one embodiment, theindirect heat exchange system is configured to indirectly transferthermal energy from the one or more heat sources 308 to the volume ofthe supercritical fluid contained within the heat transfer element 307.In one embodiment, the indirect heat exchange system includes anintermediate heat transfer element (not shown) configured to transferthermal energy from the one or more heat source 308 to the intermediateheat transfer element. In turn, the intermediate heat transfer elementmay transfer thermal energy from the intermediate heat transfer elementto the volume of the supercritical fluid contained within the heattransfer element 307.

In an embodiment, the intermediate heat transfer element may include anintermediate heat transfer loop and one or more heat exchangers. Theintermediate heat transfer loop may include any working fluid known inthe art suitable for transferring thermal energy. For example, theworking fluid of the intermediate heat transfer loop may include, but isnot limited to, a liquid salt, a liquid metal, a gas, a supercriticalfluid (e.g., supercritical CO₂) or water.

Further, as described previously herein, the heat transfer element 307of the heat transfer system 306 may intermix the supercritical fluidcontained within the heat transfer element 307 with the feedstockmaterial 305 contained within the thermochemical reaction chamber 304.In turn, upon transferring thermal energy from the heat source 308 tothe feedstock material 305 via the heat transfer element 307, thethermal energy transfer system 306 may re-circulate the supercriticalfluid coolant via return path 318.

It is noted herein that the above description of the direct and indirectcoupling between the one or more heat sources 308 and the feedstock 305is not limiting and is provided merely for illustrative purposes. It isrecognized herein that in a general sense the integration between theone or more heat sources (e.g., nuclear reactor) and the thermochemicalreaction chamber 304 may occur by transferring heat from a primary,intermediate, or ternary heat transfer system (e.g., coolant system) ofthe one or more heat sources 308 to the working fluid, such assupercritical CO₂, of the thermochemical conversion system 302. It isfurther recognized herein that this integration may be carried out usingany heat transfer systems or devices known in the art, such as, but notlimited to, one or more heat transfer circuits, one or more heat sinks,one or more heat exchangers and the like.

In one embodiment, the thermal energy transfer system 306 includes aflow control system 310. The flow control system 310 may be arranged toselectably place the supercritical fluid in thermal communication withthe volume of feedstock contained within the thermochemical reactionchamber 304. In this regard, the flow control system 310 may selectablytransfer thermal energy from the one or more heat sources 308 to thevolume of feedstock contained within thermochemical reaction chamber304. For example, the flow control system 310 may be positioned alongthe heat transfer element 307 (e.g., heat transfer loop) in order tocontrol the flow of supercritical fluid through the heat transferelement 307. In this regard, the flow control system 310 may control theflow of the supercritical fluid to the volume of feedstock 305, therebycontrolling the transfer of thermal energy to the feedstock 305.

The flow control system 310 may include any flow control system known inthe art suitable for controlling supercritical fluid flow from a firstposition to a second position. For example, the flow control system 310may include, but is not limited to, to one or more control valvesoperably coupled to the heat transfer element 307 and suitable forestablishing and stopping flow through the heat transfer element 307.For instance, the flow control system 310 may include a manuallycontrolled valve, a valve/valve actuator and the like.

In another embodiment, the flow control system 310 may couple thethermal energy from the one or more heat sources 308 to an electricalgeneration system (not shown). For example, the flow control system 310may establish a parallel coupling of heat source 308 generated heat to aturbine electric system and the thermochemical conversion system 302. Inone embodiment, the thermochemical conversion system 302 may includemultiple batch-type reaction systems, which may receive heat from theone or more heat sources 308 (e.g., nuclear reactor). In this manner, itis possible to run multiple batch processes, concurrently orsequentially, which address overall thermal and feedstock conversionneeds. In another embodiment, heat may be transferred to one or morecontinuous thermochemical reactors while being coupled in parallel toone or more turbine electric system.

In one embodiment, the system 300 includes a feedstock supply system312. In one embodiment, the feedstock supply system 312 is operablycoupled to the thermochemical reaction chamber 304 of the thermochemicalconversion system 302. In another embodiment, the feedstock supplysystem 312 provides a volume of feedstock material and water 305 to theinterior of the thermochemical reaction chamber 304. The feedstocksupply system 312 may include any supply system known in the artsuitable for transferring a selected amount of feedstock material, suchas solid material, particulate material or liquid material, from one ormore feedstock sources to the interior of the thermochemical reactionchamber 304. For example, the feedstock supply system 312 may include,but not limited, to a conveyor system, a fluid transfer system and thelike.

The feedstock supply system 312 may include separate systems fortransferring the feedstock and transferring additional water in theamount necessary for the desired reaction. In an alternative embodiment,water may be added to the feedstock prior to the transfer of thefeedstock into the reaction chamber 304. This may be done in thefeedstock supply system 312 or prior to receipt by the feedstock supplysystem 312.

A moisture control system (not shown) may be provided to determine themoisture of the feedstock and add water if necessary. Such a system mayinclude a moisture detector that continuously or periodically determinesthe moisture of the feedstock, compares the moisture to a target watercontent range and adds water if the moisture is below the target range.A dryer may also be provided in case the moisture is above the targetrange for drying the feedstock material 305.

The feedstock material 305 may include any carbonaceous material knownin the art. For example, the feedstock material 305 may include, but isnot limited to, coal, biomass, mixed-source biomaterial, peat, tar,plastic, refuse, and landfill waste. For example, in the case of coal,the feedstock may include, but is not limited to, bituminous coal,sub-bituminous coal, lignite, anthracite and the like. By way of anotherexample, in the case of biomass, the feedstock may include a woodmaterial, such as, but not limited to, softwoods or hardwoods.

It is noted herein that the ability to control temperature, pressure,reaction time, pre-treatment options, and post organic-productproduction options may allow for multiple types of carbonaceousfeedstock to be utilized within the system 300. In addition, the abilityto co-utilize or switch between types of feedstock may improve theutilization of available resources and improve the overall pitchproduction economics.

Referring again to FIG. 3, the thermochemical conversion system 302includes any thermochemical reaction chamber 304 suitable for carryingout pyrolysis. In one embodiment, the thermochemical reaction chamber304 is configured to carry out a pyrolysis reaction on the feedstock305. In another embodiment, the thermochemical reaction chamber 304includes a pyrolysis chamber. In another embodiment, the thermochemicalreaction chamber 304 includes a non-combustion or low-combustionpyrolysis chamber. The pyrolysis chamber of system 300 may encompass anythermochemical reaction chamber suitable for carrying out thethermochemical decomposition of organic molecules in the absence ofoxygen or in a low oxygen environment.

In one embodiment, the thermochemical reaction chamber 304 includes afast pyrolysis reactor suitable for converting feedstock 305, such ascoal, to reaction products including pitch. A fast pyrolysis reactor mayinclude any thermochemical reaction chamber capable of carrying out athermochemical decomposition of organic molecules in the absence ofoxygen (or in a reduced oxygen environment) within approximately twoseconds. Fast pyrolysis is generally described by Roel J. M. Westerhofet al. in “Effect of Temperature in Fluidized Bed Fast Pyrolysis ofBiomass: Oil Quality Assessment in Test Units,” Industrial & EngineeringChemistry Research, Volume 49 Issue 3 (2010), pp. 1160-1168, which isincorporated herein by reference in the entirety. Pyrolysis and fastpyrolysis are also generally described by Ayhan Demirbas et al. in “AnOverview of Biomass Pyrolysis,” Energy Sources, Volume 24 Issue 3(2002), pp. 471-482, which is incorporated herein by reference in theentirety.

In another embodiment, the thermochemical reaction chamber 304 includesa supercritical pyrolysis reactor suitable for converting feedstock 305,such as coal or biomass, to a reaction product, such as pitch. For thepurposes of the present disclosure, a ‘ supercritical pyrolysis reactor’is interpreted to encompass any reactor, reaction vessel or reactionchamber suitable for carrying out a pyrolysis reaction of feedstockmaterial using the thermal energy supplied from a supercritical fluid.In another embodiment, the thermochemical reaction chamber 304 mayinclude, but is not limited to, a fluidized bed reactor.

In another embodiment, the thermochemical reaction chamber 304 may carryout one or more extraction processes on the feedstock. In anotherembodiment, an extraction chamber operably coupled to the thermochemicalreaction chamber 304 may carry out one or more extraction processes onthe feedstock after either of the first or second stage of pyrolysis. Inone embodiment, the thermochemical reaction chamber 304 is configured toremove additional compounds from the feedstock material prior topyrolysis. For example, the thermochemical reaction chamber 304 may beconfigured to remove at least one of oils and lipids, sugars, or otheroxygenated compounds. In another embodiment, the extracted compounds maybe collected and stored for the development of additional bio-derivedproducts.

It may be advantageous to remove sugars from the feedstock material 305.It is recognized herein that sugars caramelize at elevated temperatureand may act to block the supercritical fluid, such as supercritical CO₂,from entering the cellulose structure of the feedstock material 305. Inaddition, sugars present in the thermochemical conversion system 302 mayalso act to harm downstream catalyst beds (if any). It is noted hereinthat the removal of sugars aids in avoiding the formation of oxygenatedcompounds such as, but not limited to, furfural, hydroxymethalfurfural,vanillin and the like.

In one embodiment, the thermochemical conversion system 302 may extractmaterials from the feedstock 305 at temperatures below 200° C. It isnoted herein that it is beneficial to extract sugars at temperaturesbelow 200° C. as fructose, sucrose and maltose each caramelize attemperatures below approximately 180° C. In this regard, thesupercritical fluid, through the deconstruction of cellulosic materialand the sweeping away of sugars, may serve to extract sugars from thefeedstock 305 prior to the elevation of temperatures during pyrolysis.

In another embodiment, the thermochemical reaction chamber 304 isconfigured to pre-heat the feedstock 305 prior to thermal decomposition.In another embodiment, a pre-heating chamber operably coupled to thethermochemical reaction chamber 304 is configured to pre-heat thefeedstock 305 prior to thermal decomposition. For example, thethermochemical reaction chamber 304 (or the pre-heating chamber) maypre-heat the feedstock material to a temperature at or near thetemperature necessary for liquefaction and/or pyrolysis.

In another embodiment, the thermochemical reaction chamber 304 isconfigured to pre-treat the feedstock 305 prior to thermaldecomposition. For example, the thermochemical reaction chamber 304 maypre-hydrotreat the feedstock material with hydrogen prior toliquefaction and/or pyrolysis. For instance, pre-treating the feedstockmaterial with hydrogen may aid in removing materials such as, but notlimited to, sulfur, as well as serving to donate hydrogen to reactivespecies (i.e., stabilizing free radicals).

In an alternative embodiment, not shown, the thermochemical conversionsystem 302 is separated into multiple process chambers for carrying outthe various steps of the multi-stage thermochemical process of system300. For example, in one embodiment, a first chamber is provided for thefirst stage of pyrolysis at the intermediate temperature, a second stageis provided for the second stage of pyrolysis at the pyrolysistemperature and an extraction chamber is provided for solvent contactingand extracting the solvent with the desired pitch product. The feedstock305 may be transferred between the chambers continuously or as a batchprocess.

Applicants note that while the above description points out that in someembodiments the pyrolysis reaction chambers and extraction chamber mayexist as separate chambers, this should not be interpreted as alimitation. Rather, it is contemplated herein that two or more of thethermochemical steps may each be carried out in a single reactionchamber.

In one embodiment, the thermochemical reaction chamber 304 includes amulti-stage single thermochemical reaction chamber. In one embodiment,the thermochemical conversion system 306 is configured to transfermultiple portions of the supercritical fluid across multiple temperatureranges to the volume of feedstock 305 contained within the multi-stagesingle thermochemical reaction chamber 304 to perform a set ofthermochemical reaction processes on the at least a portion of thevolume of feedstock.

In another embodiment, the thermal energy transfer system 306 isconfigured to transfer a first portion of the supercritical fluid in asecond temperature range to the volume of feedstock 305 contained withinthe single thermochemical reaction chamber 304 to perform a pre-heatingprocess on at least a portion of the volume of feedstock.

In another embodiment, the thermal energy transfer system 306 isconfigured to transfer a second portion of the supercritical fluid in afirst temperature range to the volume of feedstock 305 contained withinthe single thermochemical reaction chamber 304 to perform the firststage of pyrolysis on at least a portion of the volume of feedstock.

In another embodiment, the thermal energy transfer system 306 isconfigured to transfer a third portion of the supercritical fluid in asecond temperature range to the volume of feedstock 305 contained withinthe single thermochemical reaction chamber 304 to perform the secondstage of pyrolysis on at least a portion of the volume of feedstock.

In one embodiment, the flow and temperature of the supercritical fluidare varied spatially across the thermochemical reaction chamber 304. Forexample, in order to vary flow and/or temperature across the reactionchamber 304, multiple flows of supercritical fluid, each at a differenttemperature, may be established prior to entering the single reactionchamber. In this regard, in a vertical reaction chamber, the flow rateand temperature at a number of spatial locations, corresponding to thevarious thermochemical stages, may be varied. By way of another example,the temperature of the supercritical fluid may be varied along thelength of the thermochemical reaction chamber 304 by flowing thesupercritical fluid along the length of the thermochemical reactionchamber 304. For instance, a flow of low temperature supercritical CO₂may be combined with a flow of CO₂ at a higher temperature (e.g.,between 70 to 150° C.) to dissolve sugars. At another point downstream(e.g., 1-3 meters downstream with an average flow rate of 0.25-4 m/s),supercritical CO₂ at or above pyrolysis temperatures is mixed into thechamber. By staging the temperatures of the various thermochemicalreaction steps according to length, the flow rate may be used to controlreaction times.

It is further contemplated that two or more thermochemical steps, suchas pyrolysis, extraction and separation, are carried out in thethermochemical chamber 304, while additional steps, such as drying andpre-heating are carried out in a dedicated chamber operably coupled tothe thermochemical reaction chamber 304.

Reaction chambers may include one or more outlets 319, in accordancewith one or more embodiments of system 300. In the embodiment shown inFIG. 3, the reaction chamber 304 is provided with an outlet for removingthe feedstock residue remaining after the second stage of pyrolysis andanother outlet for removing the solvent laden with the pitch and otherdissolved pyrolysis products. In one embodiment, the outlet for thefeedstock residue remaining after the second stage of pyrolysis iscomplete is arranged to remove the residue and transfer it to a residuestorage system 314. In an embodiment, the residue storage system 314 maybe as simple as a drum, railcar, Conex box or other portable container.In an alternative embodiment, the residue may be stored in piles forlater transport.

The solvent outlet 319 transfers the solvent, in this embodiment thesCO₂, to a separation system 320. In an embodiment, the outlet includesa valve that controls the flow of gas from the reaction chamber 304 tothe separation system 320.

In an embodiment, the separation system 320 in successive steps reducesthe temperature and/or pressure to obtain different dissolvedcomponents. For example, optionally a heat rejection heat exchangercould be used before or after the separation system 320. In one of thesesteps, the pitch is condensed and transferred to a pitch extruder 326.The pitch may be stored intermediately in a holding container.Alternatively, the pitch may be immediately passed to the extruder 326upon condensing out of the sCO₂.

In an embodiment, each step corresponds to a collection chambermaintained at a different condition of temperature and pressure in whichdissolved products are allowed to condense from the solvent. Eachchamber, then, collects those products that condense at the temperatureand pressure of that chamber. In an embodiment, pitch is obtained from achamber maintained at 350° C. or greater in temperature and 7.39 MPa orgreater in pressure.

The pitch extruder, as discussed above, extrudes the pitch into fiberswhich are then allowed to cool for use directly or indirectly as carbonfiber.

Other compounds in the solvent stream removed from the reaction chamber304 are collected for further treatment or sale in a product collectionsystem 322. In one embodiment, a volatile gas separator and storagesystem may be provided as part of the product collection system 322 orthe separation system 320. The volatile gas separator may separate oneor more volatile gases from the remainder of the one or more reactionproducts. For example, the volatile gas separator may separate volatilegases such as, but not limited to, CH₄, C₂H₄, C₂H₆, CO, CO₂, H₂, and/orH₂O from the solid or liquid reaction products. It is noted herein thatthe volatile gas separator may include any volatile gas separationdevice or process known in the art. It is further recognized that thesegases may be cooled, cleaned, collected and stored for futureutilization. Volatile gases may be produced in order to provide ahydrogen source.

In the embodiment shown, the CO₂ is returned 318 to the heat source 308for reuse after the dissolved products are removed in a closed loopsystem. In an alternative embodiment the CO₂ is simply vented.

In another embodiment, not shown, the system 300 includes a heatrecovery system. In the case of recovery, the system may recover heatfrom the sCO₂ prior to or as part of the separation system 320 (or anyother appropriate sub-system of system 300) via a heat transfer loopacting to thermally couple the sCO₂ and the heat recovery system. In oneembodiment, the recovered heat may serve as a recuperator orregenerator. In another embodiment, energy may be recovered followingthe thermochemical process carried out by chamber 304. In anotherembodiment, the recovered energy may be used to pre-heat feedstockmaterial prior to thermochemical processing. In another embodiment, therecovered energy may be used to produce ancillary power (e.g.,mechanical power or electrical power) to one or more sub-systems of thesystem 300.

FIG. 4 illustrates a process flow diagram for a batch embodiment offlexible pyrolysis system that can be tuned to change the pyrolysisproducts obtained from a given feedstock. In the embodiment shown, thefeedstock will be presented as coal. However, the reader will understandthat any carbonaceous feedstock may be used such as biomass.

FIG. 4 illustrates a closed-loop CO₂ pyrolysis system similar inoperation to those described above. In the embodiment shown in FIG. 4,the pyrolysis chamber is a column 402 filled with coal 404. An inletstream of supercritical fluid such as sCO₂ enters the top of the columnand flows through the coal 404. By controlling the flow rate of sCO₂,the residence or contact time of the sCO₂ with the coal may becontrolled as is known in the art in order to control the amount ofdissolved reaction products in the sCO₂ observed in the outlet stream ofthe chamber. In an embodiment, the sCO₂ entering the pyrolysis chamber402 can range in temperature from 300-600° C. and in pressure from7.39-12 MPa so that the pyrolysis occurs with the CO₂ atmosphere in asupercritical state. Higher temperatures and pressures may also be used.

In a batch system, the pyrolysis chamber may be a simple cylindricalchamber without any internal components other than a screen to maintainthe coal in place. Multiple chambers may be provided in parallel so thatone may be in use while the char is removed from the others and they arerecharged with new coal. In an alternative embodiment, the chamber maybe provided with agitators or screws for moving the coal during thepyrolysis.

After contacting and pyrolyzing the coal 404, sCO₂ exits the bottom ofthe column 402 with dissolved pyrolysis products as described above. Theoutput sCO₂ is then passed through a recuperating and condensing circuitthat removes the dissolved pyrolysis products and then recuperates theCO₂ for reuse in the pyrolysis chamber 402. The recuperating andcondensing circuit includes a series one or more recuperators 406 thatsimultaneously cool the CO₂ stream output by the pyrolysis chamber 402while preheating the inlet/return stream of CO₂ (in which the productshave mostly been condensed out of the stream) delivered to the chamber402. In the system 400 shown, four recuperators 406 are illustrated, afirst stage recuperator 406 a, a second stage 406 b, a third stage 406 cand a fourth stage 406 d. More or fewer recuperators 406 may be used asdesired, as described below.

The recuperators 406 may be any type of heat exchanger now know or laterdeveloped. In an embodiment, for example, the recuperators 406 are eachtube-in-tube heat exchangers with the output CO₂ in the outer tube andthe cooler, inlet CO₂ stream flowing through the inner tube. However,any type of heat exchanger may be used in any configuration determinedto be beneficial or desired.

In addition to the recuperators 406, an optional final cooling heatexchanger 408 stage may be provided as part of the recuperating andcondensing circuit to perform the final reduction of temperature of theCO₂ to the desired low temperature of the circuit. This is achievedusing a coolant, such as chilled water from a chilled water system 424as shown, to perform the final cooling of the output stream. As with therecuperators 406, the final heat exchanger 408 if utilized may be anytype of heat exchanger.

As mentioned above, the supercritical conditions for CO₂ are atemperature above 31.1° C. and pressures above 7.39 MPa. In describingthe system, CO₂ will be referred to as supercritical even though at somepoints in the system the conditions may fall below the critical point ineither temperature or pressure. In those points, it should be understoodthat the CO₂ may be in a gas or liquid state depending on thetemperature and pressure conditions. Such states may occur, for example,downstream of the pyrolyzer 402 such as in the fourth recuperator 406 orthe final heat exchanger 408.

For example, in an embodiment the low sCO₂ circuit temperature may beless than 50° C. such as room temperature (20° C.) and the low pressuremay be from 6-8 MPa. Lower temperatures and pressures may also be used.In this embodiment, the CO₂ is allowed to go subcritical in order toremove as much of the pyrolysis products as possible. In an alternativeembodiment, the circuit temperatures and pressures are maintained sothat the CO₂ remains in a supercritical state throughout the system 400.

In the embodiment shown, after each heat exchanger in the circuit, thereis a condensation collection vessel 410. Each vessel is at asubsequently lower temperature, from left to right. The condensationvessel 410 may be any type of active or passive condensing apparatus.For example, in the embodiment shown the condensation vessel 410 is acold finger condenser that provides a temperature-controlled surfaceover which the CO₂ flows. This causes any pyrolysis products condensableat or above the controlled temperature to collect in the condensationvessel 410. In an alternative embodiment, instead of a cold fingercondenser a cyclone separator may be used. Other possible condensationvessels include Liebig condensers, Graham condensers, coil condensers,and Allihn condensers, to name but a few.

Where appropriate, the term ‘process stream’ will be used to refer tothe CO₂ stream in the portion of the CO₂ circuit with CO₂ flowing fromthe pyrolysis chamber 402 through the last condensation collectionvessel 410, while ‘return stream’ or ‘inlet/return stream’ will be usedto refer to the CO₂ stream flowing through the circuit from the lastcondensation vessel, through the pump 420 and, ultimately, back into thepyrolysis chamber 402. Note that the return stream may not be completelypure CO₂ but will likely contain at least trace amounts of reactionproducts, water or other compounds that are not completely collected inthe condensation vessels. The process stream, on the other hand,depending on the location within the circuit will contain at least someand possibly very large amounts of pyrolysis reaction products that willbe sequentially removed by the various condensation vessels 410.

In the embodiment shown, the different recuperators may be operated atdifferent temperatures. For example, in an embodiment the firstrecuperator 406 a may receive the process stream of CO₂ and dissolvedreaction products at about 550° C. and discharge it at 450° C. Thesecond recuperator 406 b may receive the 450° C. stream and discharge itat 300° C. The third recuperator 406 c may receive the 300° C. streamand discharge it at 150° C. The fourth recuperator 406 d may receive the150° C. stream and outputs it at 50° C.

The return stream of CO₂ is partially reconditioned by a pump/compressor420 that brings the CO₂ back up to operating pressure (e.g.,approximately 10 MPa) and a heater 422 to provide additional heat to theCO₂ to bring it up to the desired pyrolysis temperature. For example, inan embodiment, the pump/compressor 420 receives CO₂ at about 10 MPa andcompresses the stream to about 12 MPa, which provides sufficientpressure to maintain the flow through the entire CO₂ circuit without anyadditional pumps. The heater 422 may be a single heating unit ormultiple units in parallel and/or in series depending on operatorpreference. For example, in an embodiment three, separate heaters inseries are provided that receive the recuperated CO₂ stream from thefirst recuperator 406 a and heat the stream from an inlet temperature ofabout 450° C. to about 550° C. Likewise, there may be a single pump 420as shown, or multiple pumps distributed throughout the CO₂ circuit. Forexample, in an embodiment in which a portion of circuit is belowsupercritical conditions, a dedicated heater and/or compressor (notshown) may be provided purely to recondition the CO₂ to supercritical.

By providing multiple stages of pairs of heat exchangers 406, 408followed by condensation vessels 410, the pyrolysis products may befractionated and collected by condensation temperature. This allowsdesired specific fractions to be easily separated as part of therecuperation process. By providing more or fewer stages, greater orlesser differentiation of the fractions may be achieved, as well ascontrolling the makeup of each fraction.

In addition to having multiple stages of heat exchangers 406, 408followed by condensation vessels 410, further flexibility is obtainedthrough the use of a bypass circuit created by a number of bypass valve412 in the output CO₂ portion of the circuit and the inlet/return CO₂portion of the circuit. In an embodiment, one or more of the heatexchangers are equipped with bypass capability allowing that exchangerto be completely or partially bypassed by either or both of thepyrolysis output stream and the inlet/return stream. In the embodimentshown, various bypass valves 412 are provided that allow each of thedifferent stages to be either completely or partially bypassed asdesired by the operator. At any bypass valve 412, the operator mayselect how much of the input stream is directed to either outlet of thevalve. This level of flow control provides significant flexibility inthe operation of the system 400 and allows further operational controlover where in the system the various fractions of the pyrolysis productsare collected.

The pyrolysis system 400 may further be provided with additive injectionsystems for injecting additives into the CO₂ inlet/return stream priorto delivery to the pyrolysis chamber 402. In the embodiment shown, twoadditive injection systems are shown, each including an injection pump414 and an additive supply 416. Examples of additives, described ingreater detail above, include H₂, H₂O, formic acid, and tetralin. In anembodiment, the injection pump 414 is an HPLC injection pump.

In yet another embodiment (not shown), bypass valves 412 may be providedto allow one or more condensation vessels 410 to be bypassed. Thisallows collection of reaction products to be combined into fewer vesselsas desired, thus further increasing the flexibility of the system 400.

A controller 430 is illustrated in FIG. 4. In an embodiment, thecontroller 430 is a programmable logic controller configured to monitorand control the pyrolysis system 400 to achieve desired results.Controllers may be implemented in many different manners, from purposebuilt hardware controllers to general purpose computing devicesexecuting control software. Process controllers are well known in theart and any suitable controller design or combination of designs nowknown or later developed may be used.

The controller 430 controls the distribution of the flow of the processstream and the return stream through the various stages of recuperators.In this way, the inlet and outlet temperatures of the streams at eachstage may be altered. The heat transfer equations governing the heatexchange between hot and cold streams in a heat exchanger are well knownand any form of these equations may be used by the controller todetermine the distribution of the flows among the stages in order to getspecific temperatures at specific locations in the CO₂ circuit. Forexample, one basic heat exchanger equation that may be used is a generalcounterflow heat exchange equation describing the transfer of heatacross a:{dot over (m)} _(a) c _(pa)(T _(a1) −T _(a2))={dot over (m)} _(b) c_(pb)(T _(b2) −T _(b1))where {dot over (m)}_(a) is the mass flow rate of the process stream,c_(pa) is the specific heat of the process stream, T_(a1) is the inlet(high) temperature of the process stream entering the recuperator stage,T_(a2) is the outlet (low) temperature of the process stream, {dot over(m)}_(b) is the mass flow rate of the return stream, c_(pb) is thespecific heat of the return stream, T_(b1) is the inlet (low)temperature of the return stream entering the recuperator stage, andT_(b2) is the outlet (high) temperature of the return stream. From theabove equation, as is known in the art, additional equations can bederived which mathematically describe the performance of therecuperator, often in terms of an overall heat transfer coefficient forthe recuperator based on its dimensions and characteristics. In manycases the performance equations for a heat exchanger may be provided bythe manufacturer. Such equations, as necessary, are solved by thecontroller to determine how to distribute the flow of the streamsthrough the recuperator stages in order to achieve the goals set by theoperator, examples of which are provided below.

In an embodiment the controller 430 is connected and capable ofcontrolling the bypass valves 412, the heater 422, the chilled watersystem 424, additive pumps 414, and other components of the system 400.In addition, the controller 430 may be connected to or otherwise receiveinformation or signals from one or more monitoring devices 426, fromwhich the controller 430 receives data regarding the status of thesystem 400.

FIG. 4 illustrates several monitoring devices 426 at various locationsthroughout the system 400. Monitoring devices 426 may be any type ofprocess monitor, analyzer, or sensor such as, for example, flow sensors,temperature sensors, pressure sensors, scales, pH sensors,spectrometers, photo-ionization detectors, gas chromatographs, catalyticsensors, infra-red sensors and flame ionization detectors, to name but afew. Monitoring devices 426 may be located anywhere in the system 400 asdesired. For example, in an embodiment a gas chromatograph may be usedto periodically or continuously monitor and determine the differentcompounds and their relative amounts in the reaction products in thesCO₂ leaving the reaction chamber 402. Alternatively, liquid levelsensors on each condensation vessel may be provided and from there datathe relative production rate of each recuperator stage's condensates maybe determined.

Based on information received from the monitoring devices 426, thecontroller 430 may change the flow through one or more bypass valves andthe temperatures of one or more streams to obtain a desired hydrocarboncondensate fraction (i.e., range of molecular weights) in one or more ofthe condensate vessels. For example, in an embodiment the controller maybe directed to separate and recover hydrocarbons having boiling pointsfrom 300 to 350° C. In this embodiment, the flow through the variousbypass valves may be adjusted so that the process stream is dischargedfrom the first recuperator 406 a at a temperature of 350° C. (as opposedto 450° C. as mentioned above) and discharged from the secondrecuperator 406 b at a temperature of 300° C. This may be achieved bybypassing a portion of the return stream around the second recuperator406 b so that a relatively larger and cooler return stream is driventhrough the first recuperator 406 a, increasing the relative amount ofcooling performed by the first stage. In this way, reaction productswith boiling points above 350° C. are collected in the condensate vessel410 between the first recuperator 406 a and the second recuperator 406 bwhile reaction products having boiling points from 300 to 350° C. arecollected in the condensate vessel 410 following the second recuperator406 b.

As can be seen by the above example, through the use of the controller430 and flexibility achieved by the system's design, the operatingconfiguration of the system 400 may be changed in real time to achievedifferent goals. In addition, by basing the control of the system 400 onreal-time knowledge reported by the sensors and monitoring devices, thesystem 400 can adjust over time in response to changing conditions suchas changing feedstock quality. In this aspect, through the controller430 and the multiple stages of recuperators and condensation vessels,the system 400 may be easily configured to separate and collectdifferent fractions of hydrocarbons into different condensation vessels.By providing more stages, even more differentiation may be provided asrequired. Because the controller 430 can easily reconfigure the bypassvalves 412, the system 400 is uniquely capable of handling differentoutput requirements or changes in feedstock characteristics.

In addition, the controller 430 may also be used to control and optimizethe reaction products that are obtained from the pyrolysis reaction. Forexample, in an embodiment the controller 430 may directly or indirectlycontrol the temperature and/or the pressure in the reaction chamber 402to change the relative amounts of different reaction products. In anembodiment, changes in temperature or pressure in the reaction chambermay be done in real-time based on monitoring information received fromthe sensors and monitoring devices. For example, monitoring dataindicative of the type and amount of different reaction products in thesCO₂ leaving the reaction chamber 402 may be provided to the controller430. In response to preset goals, such to optimize a subset of reactionproducts (e.g., maximize production of reaction products having boilingpoints from 250 to 350° C.), the controller 430 may then iterativelychange the temperature and/or pressure in the reaction chamber until anoptimized profile of reaction products is obtained based on the currentgoals of the system 400.

FIGS. 5A-5C illustrate the experimental performance of an embodiment ofthe system shown in FIG. 4. In the FIGS., the system is alternatelyreferred to as a multistage supercritical liquefaction system. In theexperiment, an embodiment of the system shown in FIG. 4 was created at abench scale using four recuperators and a final chilled water heatexchanger as illustrated. A 1 kg sample of Power River Basinsubbituminous coal was placing in a column and pyrolyzed using sCO₂ asdescribed above. A fine mesh screen was provided at the bottom of thecolumn to prevent solids from exiting from the chamber.

For startup, the bypass circuit was used to isolate the pyrolysischamber until the system reached the desired thermal conditions. Afterthe loop achieved test temperatures, the bypass was disabled and thepyrolysis chamber was placed in the loop. The outlet temperature of thesCO₂ leaving the pyrolysis chamber was approximately 490° C. and theinlet temperature of the sCO₂ delivered to the pyrolysis chamber wasapproximately 500° C. The pressure of the sCO₂ in the pyrolysis chamberwas approximately 10 MPa and the mass flow rate of sCO₂ circulatingthrough the circuit was between 4.5 and 10 kg/min during the experiment.The system was operated without bypassing any of the five heatexchangers such that the full flow of CO₂ passed through eachexchanger/condensation vessel stage. The condenser vessels were coldfingers and designated as Bottles 1-5 maintained at the temperaturesshown in FIG. 5. The system was operated for a period of time then thecondensed pyrolysis products from the condensation vessels wereanalyzed.

FIG. 5A illustrates a representative liquid yield obtain from pyrolyzinga batch of coal by condensation vessel temperature. The condenservessels were cold fingers and designated as Bottles 1-5 maintained atthe temperatures shown in FIG. 5A.

Mass spectroscopy was performed on the condensate fractions obtain fromBottles 2 and 5. FIG. 5B shows the results for Bottle 2 and FIG. 5Bshows the results for Bottle 5. As expected the results show asubstantially higher molecular weight product distribution was condensedin the higher temperature Bottle 2 than was obtained in the lowertemperature Bottle 5. This illustrates that the multistage separationsystem is successful in generating and fractionating different pyrolysisproducts from a carbonaceous feedstock.

FIG. 6 illustrates an embodiment of a broad method for pyrolyzingcarbonaceous feedstock to obtain reaction products using CO₂. Theembodiment shown is discussed in terms of an ongoing process thatreconditions and recycles the CO₂ for reuse in a closed loop. Theprocess in FIG. 6 is illustrated as beginning with a contactingoperation 602. In the contacting operation 602 a carbonaceous feedstockis maintained in contact with supercritical carbon dioxide for somecontact period at a pyrolysis temperature and pressure sufficient toboth maintain the CO₂ in a supercritical state and at which pyrolysisoccurs. The resulting pyrolysis causes at least some of the feedstock tobe converted into char and generates some amount of pyrolysis reactionproducts which are dissolved into the CO₂.

The contact period, or residence time, used may be selected by theoperator. The contacting may be static in that the CO₂ is not flowingthrough the contacting chamber during the pyrolysis. Rather, the chamberis charged with CO₂ and the feedstock and then allowed to react, with orwithout internal agitation or other mixing. In this case, the contacttime is the time that the CO₂ is supercritical and within the contactingchamber with the feedstock. Alternatively, the contacting may be dynamicin that the CO₂ is constantly flowing through the chamber containing thefeedstock. In the dynamic contacting, the residence time is calculatedfrom the flowrate of CO₂ and the volume of the contacting chamber.

The chemical makeup of the pyrolysis reaction products can varied to acertain extent by changing the pyrolysis conditions. For example, arelatively higher temperature and pressure used in the contactingoperation 602 may favor the generation of some reaction products (e.g.,heavier hydrocarbons such as oils) over others (e.g., mid-weight oils orlighter hydrocarbon gases). In addition, additives such as water, formicacid, hydrogen, or some other hydrogen donor may be used to increase theavailability of hydrogen during the pyrolysis, which will also changethe chemical makeup of the reaction products. Other additives may alsobe used to affect the pyrolysis reaction and vary the chemical makeup ofthe reaction products.

After the contact time, the supercritical CO₂, now containing dissolvedpyrolysis reaction products, is separated from the char in a separationoperation 604. The separation operation may take the form of removingthe char from the CO₂ or removing the CO₂ from the char.

After the separation operation 604, the supercritical CO₂ is then cooledin a first cooling operation 606 to a first temperature and a firstpressure. For example, in an embodiment the pyrolysis temperature andpressure is 540° C. and 11 MPa, respectively, and the first temperatureand first pressure is 450 and 10.9 MPa. The first cooling operation 606may include reducing the temperature or the temperature and the pressureof the CO₂ from the pyrolysis temperature and pressure used in thecontacting operation 602. In addition, although referred to as thecooling operation 606 in an embodiment the ‘cooling’ may consist of onlyreducing the pressure of the CO₂ while maintaining the temperature at orclose to the pyrolysis temperature. Regardless of whether thetemperature, the pressure or both are reduced, the cooling operation 606causes the solubility of the dissolved reaction products to change andany reaction products that are no longer soluble in the CO₂ and thefirst temperature and pressure will condense out of the CO₂ as acondensate.

As part of or after the first cooling operation 606, the condensategenerated by the first cooling operation 606 may be collected and storedfor later use. Contents of this condensate will be determined by thereaction products generated by the pyrolysis reaction and the firsttemperature and pressure of the first cooling operation 606. Thus, asdescribed above, through selection of the first temperature andpressure, the chemical makeup of the condensate generated by the firstcooling operation 606 can be controlled to obtain a specific fraction ofthe pyrolysis reaction products. Once the temperatures are known, in anembodiment the heat exchanger equations can be used to determine therelative flow rates of the return stream and process stream through thedifferent recuperators necessary to achieve those temperatures and,thus, the desired condensate. From this information the controller canthen set the positions of the bypass valves as necessary to obtain thedetermined flow rates.

The CO₂ with the remaining reaction products is then subjected to asecond cooling operation 608. Similar to the first cooling operation606, the second cooling operation 608 reduces the CO₂ from the firsttemperature and pressure to a second temperature and pressure. Again,this may include reducing the temperature, the pressure or both of theCO₂. The second cooling operation can be performed using the sameequipment as the first cooling operation 606 or by passing the CO₂ to asecond set of equipment (e.g., heat exchanger, cooling vessel, etc.) inwhich the second cooling operation is performed.

As part of or after the second cooling operation 608, the condensategenerated by the second cooling operation 608 may be collected andstored for later use. Contents of this second condensate will bedetermined by the reaction products generated by the pyrolysis reaction,the first temperature and pressure used in first cooling operation 606,and the second temperature and pressure of the second cooling operation608. Thus, as described above, through selection of the first and secondtemperatures and pressures, the chemical makeup of the condensategenerated by the second cooling operation 606 can be controlled toobtain a specific fraction of the pyrolysis reaction products. Once thetemperatures are known, in an embodiment the heat exchanger equationscan be used to determine the relative flow rates of the return streamand process stream through the different recuperators necessary toachieve those temperatures and, thus, the desired condensate. From thisinformation the controller can then set the positions of the bypassvalves as necessary to obtain the determined flow rates.

Additional cooling operations (not shown) can be performed. By usingadditional cooling operations the fractionation and collection of thereaction products can be tightly controlled. For example, 25 coolingoperations can be used to obtain very finely fractionated condensates.Any number of cooling operations may be used as desired depending on theoperator's goals. With reference to FIG. 4 that shows a system with apotential of five cooling operations, the chemical makeup of thecondensates of each of the five stages can be varied by changing therelative temperatures and pressures of the operations. For example, inone configuration, the first four cooling operations may be done withvery narrow temperature and/or pressure differences—e.g., the firsttemperature may be 10° C. less than the pyrolysis temperature, thesecond temperature 20° C. less, the third 30° C. less and the fourth 40°C. less, while the last temperature may be 30° C., a configuration thatwould fractionating higher temperature reaction products (that is,reaction products that condense out of the CO₂ at a higher temperature).In another configuration, the temperature differences may be more evenbetween stages and in yet another configuration the temperatures may befocused to fractionate lower temperature products. Thus, as part of thismethod, the temperatures and pressures of the different coolingoperations may be controlled to obtain specific desired fractions of thereaction products.

Finally the CO₂ is recycled and reused for additional pyrolysis is areuse operation 610. The reuse may be done in a continuous system inwhich the CO₂ is continuously flowing in a loop such as that shown inFIG. 4. Alternatively, the CO₂ may be stored for reuse later in a batchor semi-batch system.

As part of the method 600, the CO₂ may be maintained in thesupercritical state throughout the entire method. Alternatively, the CO₂may be taken to a subcritical state, for example in a final coolingoperation, in order to condense and remove as much of the reactionproducts as possible, before the CO₂ is returned to the supercriticalstate in the reuse operation 610.

FIG. 7 is a more detailed embodiment of a method for pyrolyzing coalwith supercritical CO₂. While the method 600 of FIG. 6 is more broadlywritten to cover any batch, semi-batch or continuous pyrolysis process,the method 700 of FIG. 7 is more specific to a continuous pyrolysisprocess that fractionates pyrolysis products from coal and recycles theCO₂ in a continuously flowing loop.

In the embodiment shown in FIG. 7, the method 700 begins with flowing aninlet stream of carbon dioxide (CO₂) into a reaction chamber containingcoal in a supercritical CO₂ injection operation 702. In an embodiment,the inlet CO₂ stream's temperature is from 300-600° C. and pressure isfrom 7-12 MPa.

The reaction chamber is maintained at a pyrolysis temperature andpressure sufficient to maintain the CO₂ in the reaction chamber in asupercritical state. This is illustrated in FIG. 7 by the pyrolysisoperation 704. The pyrolysis operation 704 may include activelycontrolling the temperature and pressure of the reaction chamber. Forexample, an internal or external heater may be used to add heat directlyto the reaction chamber to control its temperature. Likewise, thepressure may be controlled by adjusting the flow rate of the inlet andoutlet CO₂ streams. Alternatively, the temperature and pressure of thereaction chamber may be indirectly controlled solely by controlling thetemperature and flow rate of the inlet stream. Thus, the coal ispyrolyzed to obtain a char and supercritical CO₂ containing dissolvedpyrolysis products in the pyrolysis operation 704. As discussed abovewith reference to FIG. 6, the chemical makeup of the reaction productsmay be controlled to an extent by changing the temperature and pressurein the reaction chamber and also through the use of certain additives.

After a contact period determined by the CO₂ flow rate through thereaction chamber and the volume of CO₂ in the chamber, the supercriticalCO₂ containing dissolved pyrolysis products then flows as a reactoroutlet stream from the reaction chamber via an outlet in an outletstream discharge operation 706.

The outlet stream is then passed to first recuperator in a firstrecuperation and collection operation 706 a. In this operation 706 a,the reactor outlet stream is cooled in the first recuperator bytransferring heat to a return stream of CO₂ on its way back to thereaction chamber. The outlet stream is cooled to a first temperatureless than the pyrolysis reaction temperature based on the temperaturesand flow rates of the two CO₂ streams, i.e., the outlet stream and thereturn stream, passing through the first recuperator.

The act of cooling the outlet stream causes the dissolved reactionproducts which condense at temperatures greater than the firsttemperature, if any, in the outlet stream to condense out of the CO₂.The first recuperation and collection operation 706 a includescollecting this first stage condensate in a collector such as acollection vessel as shown in FIG. 4. It also includes discharging afirst stage CO₂ effluent stream that contains any dissolved reactionproducts not removed as a first stage condensate.

It should be pointed out that not all of the outlet stream may betreated in the first recuperation and collection operation 706 a. In anembodiment some portion of the outlet stream may be sent to a laterstage recuperator and treated in a later recuperation and collectionoperation. This diversion of some of the outlet stream may be done tocontrol the chemical makeup of the condensates obtained from thedifferent stages.

The first stage CO₂ effluent stream is then passed to second recuperatorin a second recuperation and collection operation 706 b. In thisoperation 706 b, the reactor first stage CO₂ effluent stream is cooledin the second recuperator by transferring heat to the return stream ofCO₂ on its way back to the reaction chamber. The first stage CO₂effluent stream is cooled to a second temperature less than the firsttemperature based on the temperatures and flow rates of the two CO₂streams, i.e., the first stage CO₂ effluent stream and the returnstream, passing through the second recuperator.

Again, the act of cooling the outlet stream causes those dissolvedreaction products remaining in the first stage CO₂ effluent stream whichcondense at temperatures higher than the second temperature, if any, tocondense out of the CO₂. The second recuperation and collectionoperation 706 b includes collecting this second stage condensate in acollector such as a collection vessel as shown in FIG. 4. It alsoincludes discharging a second stage CO₂ effluent stream that containsany remaining dissolved reaction products not removed as a second stagecondensate.

Again, not all of the first stage CO₂ effluent stream need be passed tothe second recuperator and some portion of the first stage CO₂ effluentstream may be diverted to a later recuperation and collection operationin order to change the chemical makeup of later stage condensates.

Any number of additional recuperation and collection operations may beperformed in the method 700. This is illustrated in FIG. 7 by theellipsis and the n-stage recuperation and collection operation 706 n.Each of the recuperation and collection operations 706 a-n may beidentical except for the operational temperature and pressures of thetwo CO₂ streams involved. The condensates recovered from each of theoperations 706 a-n may be controlled by diverting portions of theprocess stream and/or return stream around and to various operations 706a-n to obtain desired condensates. The distribution of flow through thedifferent recuperation and collection operation 706 a-n may be manuallycontrolled or automatically controlled by a controller in order tocollect different fractions at different stages as described above.

Note that one or more of the operations 706 a-n, such as for example thefinal recuperation and collection operation 706 n as in FIG. 4, may notinclude recuperating heat from the process stream. That is, rather thanpassing heat to the return stream of CO₂ and effectively recycling thatenergy, the heat may simply be removed, such as by transferring it to acold water stream, and either discarded or recycled for another purpose.

In addition, not all of the recuperation and collection operations 706a-n need include the collection of a condensate in a separate vessel.Rather, some condensates could be directed into the following stagerecuperators for later collection in a downstream recuperation andcollection operation.

After the last recuperation and collection operations 706 n, the finalstage CO₂ effluent steam is then reconditioned by passing it as thereturn stream through the various recuperation stages in areconditioning operation 708. The reconditioning operation 708 mayinclude compressing the return stream and/or heating the return streamat one or more points in the system's CO₂ return circuit. For example,in FIG. 4 the return stream is compressed by the pump 420 right afterthe fifth recuperation and collection operation (in that case not a truerecuperation as the heat is removed using a cold water stream) andheated by heater 422 just prior to being injected into the reactionchamber 402.

Note that the reconditioning operation 708 may or may not clean anyremaining reaction products from the CO₂. In an embodiment, some traceamounts of reaction products and/or other compounds such as water remainin the CO₂ return stream when it is injected into the reaction chamber.

After reconditioning, the CO₂ return stream is then injected into thereaction chamber as the inlet stream in the injection operation 402.This is illustrated in FIG. 7 by the return arrow from thereconditioning operation 708 to the injection operation 702.

FIG. 8 illustrates an embodiment of a method for improving mesophasepitch for carbon fiber production using supercritical carbon dioxide.The method uses as a feedstock some or all of a coal tar product havingat least some mesophase pitch, including those discussed above. In analternative embodiment, any feedstock having at least some mesophasepitch, whether derived from coal, any other biomass, or a hydrocarbonmaterial, may be used as the feedstock. For the remainder of thisdescription, ‘coal tar’ is the material/oils that come from pyrolysis orcoking of coal. Material extracted from the coal tar is referred to as‘coal tar pitch’.

In general, the following method 800 improves the quality of the coaltar product by isolating and recovering a high molecular weight (MW)coal tar, for example, from the system 400 as shown in FIG. 4 above bycontacting the feedstock with a mixture of a supercritical fluid solventand a co-solvent. By high molecular weight it is meant a compoundshaving a molecular weight of 1,000 amu or more. High MW hydrocarbons ofcoal tar are a mesophase precursor material. While the supercriticalfluid may be any supercritical fluid as described above, and theco-solvent may be any co-solvent (such as, for example, benzene, xylene,tetralin, tetrahydrofuran, pyridine, quinolone, pyridine, quinolone, andthe like) or mixtures of co-solvents, the rest of this description willdiscuss the specific embodiment of a supercritical carbon dioxide(sCO₂)/toluene solvent/co-solvent combination. One of skill in the artwill recognize that this disclosure is not limited to the specificembodiment described below.

The method 800 begins (operation 802) with placing feedstock coal tar ina reactor vessel, such as vessel 404 above. In an embodiment anyparticular fraction, or combination of fractions, of coal tar may beused as the initial feedstock. For example, in an embodiment all of thecoal tar produced by the system 400 of the published application may beused. Alternatively, all of the coal tar that condenses out above somethreshold temperature may be used. For example, all coal tar thatcondenses out at or above 50° C., 100° C., 150° C., or 200° C. may beused. Alternatively, coal tar that condenses out between some definedrange of temperatures may be used.

The reactor vessel is then raised to operational temperature andpressure (as described above) and the sCO₂/toluene solvent is passedthrough the reactor vessel 404 and condensation circuit in asCO₂/toluene extraction operation 804. The toluene soluble (TS) fractionis collected and recovered from the flowing sCO₂/toluene solvent leavingthe reaction vessel by the condensation circuit. The flow is maintainedfor some period of time such as, for example, one minute, one hour, twohours, four hours, ten hours, 24 hours, etc. selected by the operator.The time period may be fixed or may be determined based on the amount ofTS fraction material recovered over time. For example, when the amountTS fraction material per minute falls below a threshold, the extractionmay be considered to be completed. After this time period, the flow isterminated and the reactor conditions are reduced to below supercriticalconditions.

Optionally, the material remaining in the reaction vessel may then bewashed with toluene as final step in the operation 804. Alternatively, asolvent other than toluene or a combination of multiple solvents (e.g.,toluene and xylene) after the temperature and pressure conditions havebeen reduced to below supercritical conditions.

After the sCO₂/toluene extraction operation 804, the toluene insoluble(TI) fraction remaining in the reaction vessel may be washed withquinoline in a quinoline soluble fraction extraction operation 806. Inan alternative embodiment, the extraction operation 806 may be done in adifferent reaction vessel necessitating a transfer operation betweenvessels.

In one embodiment of this operation 806, quinoline is added to thematerial remaining in the vessel and held at some temperature andpressure for some period of time. In an alternative embodiment,quinoline is circulated through the reaction vessel held at sometemperature and pressure for some period of time. After the desiredperiod of time, for any period of time, for example, less than or up toone minute, one hour, two hours, four hours, ten hours, 24 hours, etc.,the quinoline is removed thereby removing any quinoline-soluble (QS)material leaving the quinoline insoluble (QI) material behind in thereaction vessel.

The quinoline along with any dissolved QS components are then distilled,for example using rotary evaporation, in a distillation operation toseparate the quinoline from the QS compounds. The QS compounds recoveredfrom the distillation of the quinoline, referred to herein as the QSfraction, represent an improved coal tar product suitable for theproduction of anisotropic mesophase pitch suitable for carbon fiberformation/spinning.

After distillation, the QS fraction is heat treated to make mesophasepitch before adding to an extruder. This heat treatment operation 807generates mesophase structure or increases the amount mesophase materialif mesophase material is already present. In an embodiment, the heattreatment operation 807 may be performed under vacuum, atmospheric, orpressurized condition (e.g., from 1.01 atm to 500 atm) and includesheating the QS fraction to from 300 to 400° C. and holding it at thattemperature for some period of time sufficient to generate mesophasestructure. For example, in one embodiment, temperature-controlled sCO₂may be used to heat the QS fraction in a reactor vessel. Through thisstep, a mesophase structure (70-100%) is produced. The operation 807 mayalso create some additional quinoline insoluble (QI) material which maybe separated from the QS fraction as shown before the next operation.This may be done by performing a second extraction operation 806.

In an alternative embodiment, the heat treatment operation 807 may heatthe QS fraction to any temperature from 200 to 800° C. for any period oftime, for example, less than or up to one minute, one hour, two hours,four hours, ten hours, 24 hours, etc., selected by the operator. Thetime period may be fixed or may be determined based on the amount ofmesophase generation.

The QS fraction is then thoroughly mixed and extruded under fixedconditions in a compounding operation 808. This may be done using anycommercial compounder or extruder such as, for example, a HAAKE™ MiniLab3 Micro Compounder or a Pharma 11 Twin-screw extruder (both by ThermoScientific®). In this operation, the QS fraction is thoroughly mixedunder supercritical conditions in a sCO₂ environment for a desiredamount of time. After the desired amount of mixing, the QS fraction andsCO₂ mixture is extruded. As the material leaves thecompounder/extruder, at temperature, the sCO₂ solvent evaporates out ofthe mixture carrying away any compounds solubilized into the sCO₂leaving fibers of the mesophase pitch. It is believed that the remainingextruded material will be mostly if not entirely mesophase pitch and forthis reason it is referred to as the mesophase fraction. Without beingbound to any particular theory, it is also believed that the extrusionat temperature with the sCO₂ may potentially serve as both oxidizer andcatalyst to residual unwanted light MW compounds (representingimpurities in the mesophase pitch solution) that can ultimately formcoke or poor crystallization upon graphitization resulting in poorcarbon fiber quality.

In the compounding operation 808 described above, the mixing andextrusion are performed at the same time as a combined process. In analternative embodiment, the mixing and extrusion could be treated asseparate operations. In this embodiment, the mixing is performed undersupercritical conditions and in a sCO₂ environment for such time asnecessary to consider the QS fraction fully mixed. After it is fullymixed, the QS fraction and sCO₂ is then passed through an extruder whichcauses the sCO₂ to separate from the mesophase fraction and createfibers of mesophase fraction. The pressure, partial pressure,concentration of the sCO₂ may be adjusted prior to extrusion. Theseparated sCO₂, which will likely contain at least some dissolved low MWcompounds, is removed as a sCO₂ fraction.

In yet another embodiment, the extrusion process may be performed withsome amount of CO₂ solvent and co-solvent (e.g. quinolone or toluene)from the sCO₂/toluene extraction operation 804 with the mesophasefraction. The mesophase fraction may then be melt spun or otherwiseextruded directly into fibers as is known in the art.

In yet another embodiment, the extrusion process may be replaced by asimple separation process in which the sCO₂ fraction is separated fromthe mesophase fraction. After this separation, the mesophase fractionmay then be melt spun or otherwise extruded directly into fibers as isknown in the art. Alternatively, the mesophase fraction may be sold asis or used for other purposes than making fibers.

The fibers of mesophase fraction may be further stabilized in anoptional stabilization operation 810. Current stabilization practicesextrude and pull the fiber through a series of medium (˜200-300° C.)temperature oxidation ovens. One purpose of conventional stabilizationis to oxidatively remove residual light MW materials prior tographitization. Because the prior operations in the method 800,particularly the sCO₂/toluene extraction operation 804 and thecompounding operation 808, are anticipated to remove many, if not mostor all, of the lower molecular weight compounds, the sCO₂ processdescribed above may remove the need for a stabilization operation 810altogether or, alternatively, reduce the amount of time necessary forsufficient stabilization.

After stabilization, an optional carbonization operation 812, as isknown in the art, may be performed. Carbonization is the processremoving all nonorganic elements by heating the fibers in an oxygen-freeenvironment and creates a crystalline carbon structure in the fibers.Due to the earlier extractions, it may be that the mesophase fractionwill be sufficiently devoid of nonorganic elements to eliminate the needfor a carbonization operation, or may reduce the time necessary for thecarbonization to be performed.

A graphitization operation 814 may then be performed on the mesophasefraction as is known in the art as the final step in creating the carbonfiber. Graphitization involves treating the fibers at high temperaturesto improve the alignment and orientation of the crystalline regionsalong the fiber direction. Having the crystalline regions aligned,stacked, and oriented along the fiber direction increases the overallstrength of the carbon fiber.

Unless otherwise indicated, all numbers expressing quantities ofingredients, properties such as molecular weight, reaction conditions,and so forth used in the specification and claims are to be understoodas being modified in all instances by the term “about.” Accordingly,unless indicated to the contrary, the numerical parameters set forth inthe following specification and attached claims are approximations thatmay vary depending upon the desired properties sought to be obtained.

Notwithstanding that the numerical ranges and parameters setting forththe broad scope of the technology are approximations, the numericalvalues set forth in the specific examples are reported as precisely aspossible. Any numerical value, however, inherently contain certainerrors necessarily resulting from the standard deviation found in theirrespective testing measurements.

It will be clear that the systems and methods described herein are welladapted to attain the ends and advantages mentioned as well as thoseinherent therein. Those skilled in the art will recognize that themethods and systems within this specification may be implemented in manymanners and as such are not to be limited by the foregoing exemplifiedembodiments and examples. In this regard, any number of the features ofthe different embodiments described herein may be combined into onesingle embodiment and alternate embodiments having fewer than or morethan all of the features herein described are possible.

While various embodiments have been described for purposes of thisdisclosure, various changes and modifications may be made which are wellwithin the scope contemplated by the present disclosure. For example, inan embodiment the quinoline extraction operation 806 may be omitted andthe TI fraction sent directly to the heat treatment operation 807.Numerous other changes may be made which will readily suggest themselvesto those skilled in the art and which are encompassed in the spirit ofthe disclosure.

What is claimed:
 1. A method comprising: contacting coal tar containingat least some mesophase pitch precursor with a supercritical carbondioxide (sCO₂) and toluene mixture, thereby removing at least sometoluene soluble components from the coal tar to obtain a tolueneinsoluble fraction; after the contacting operation, separating the sCO₂and toluene mixture from the toluene insoluble fraction; washing thetoluene insoluble fraction with quinoline to obtain a quinoline andquinoline soluble fraction mixture of the toluene insoluble fraction;separating the quinoline from the quinoline soluble fraction; mixing thequinoline soluble fraction with sCO₂ to obtain a sCO₂/quinoline solublefraction mixture.
 2. The method of claim 1, wherein the contactingoperation further comprises: passing the sCO₂/quinoline soluble fractionmixture through an extruder, thereby separating the sCO₂ from thequinoline soluble fraction to obtain fibers of mesophase pitch.
 3. Themethod of claim 1 further comprising: after the separating operation,performing a toluene wash on the toluene insoluble fraction therebyremoving additional soluble material from the toluene insolublefraction.
 4. The method of claim 1 wherein separating the quinoline fromthe quinoline soluble fraction further comprises: distilling thequinoline and quinoline soluble fraction mixture.
 5. The method of claim1 wherein separating the quinoline from the quinoline soluble fractionfurther comprises: evaporating the quinoline to obtain the quinolinesoluble fraction mixture.
 6. The method of claim 1 further comprising:heating the quinoline soluble fraction to from 300 to 400° C.
 7. Themethod of claim 1 further comprising: heating the quinoline solublefraction to from 300 to 400° C. for less than 24 hours.
 8. The method ofclaim 1 further comprising: performing a stabilization operation on thefibers of mesophase pitch.
 9. The method of claim 1 further comprising:performing a carbonization operation on the fibers of mesophase pitch.10. The method of claim 1 further comprising: performing agraphitization operation on the fibers of mesophase pitch.
 11. Themethod of claim 1, further comprising: passing the sCO₂ and toluenemixture through a reactor vessel containing the coal tar; and whereinthe washing operation includes washing the toluene insoluble fraction inthe reactor vessel.
 12. The method of claim 11 further comprising:circulating the quinoline through the reactor vessel for up to 24 hoursbefore separating the quinoline from the quinoline soluble fraction. 13.The method of claim 1 further comprising: heating the quinoline solublefraction to from 200 to 800° C.
 14. The method of claim 6, wherein theheating operation further comprises: contacting the quinoline solublefraction with sCO₂ heated to a temperature between 300 to 400° C. 15.The method of claim 6 further comprising: after the heating operation,separating at least some quinoline insoluble material from the quinolinesoluble material.
 16. A method of manufacturing carbon fiberscomprising: contacting coal tar containing at least some mesophase pitchprecursor with a supercritical carbon dioxide (sCO₂) and toluenemixture, thereby removing at least some toluene soluble components fromthe coal tar to obtain a toluene insoluble fraction; after thecontacting operation, separating the sCO₂ and toluene mixture from theinsoluble coal tar fraction; after the separating operation, mixing thetoluene insoluble fraction with sCO₂ to obtain a sCO₂/toluene insolublefraction mixture; and passing the sCO₂/toluene insoluble fractionmixture through an extruder, thereby separating the sCO₂ from thetoluene insoluble fraction to obtain fibers of mesophase pitch.
 17. Themethod of claim 16 further comprising: washing the toluene insolublefraction with quinoline to obtain a quinoline and quinoline solublefraction mixture and a quinoline insoluble fraction of the tolueneinsoluble fraction; separating the quinoline from the quinoline solublefraction of the toluene insoluble fraction; and mixing the quinolinesoluble fraction of the toluene insoluble fraction with sCO₂ to obtainthe sCO₂/toluene insoluble fraction mixture.
 18. The method of claim 17further comprising: heating the quinoline soluble fraction of thetoluene insoluble fraction to from 300 to 400° C. for less than 24 hoursbefore mixing the quinoline soluble fraction of the toluene insolublefraction with sCO₂.
 19. The method of claim 18, wherein the heatingoperation further comprises: contacting the quinoline soluble fractionwith sCO₂ heated to a temperature between 300 to 400° C. for up to 24hours.
 20. A method of manufacturing carbon fibers comprising:contacting coal tar containing at least some mesophase pitch precursorwith a supercritical fluid solvent and co-solvent mixture, therebyremoving at least some soluble components from the coal tar to obtain aninsoluble coal tar fraction; after the contacting operation, separatingthe supercritical fluid solvent and co-solvent mixture from theinsoluble coal tar fraction; after the separating operation, mixing theinsoluble coal tar fraction with sCO₂ to obtain a sCO₂/insolublefraction mixture; and passing the sCO₂/ilinsoluble fraction mixturethrough an extruder to obtain fibers of mesophase pitch; wherein thesupercritical fluid solvent is selected from one or more of carbondioxide, water, methane, nitrous oxide, ethane, propane, ethylene,propylene, methanol, ethanol, and acetone and the co-solvent is selectedfrom one or more of benzene, xylene, tetralin, tetrahydrofuran,pyridine, quinolone, pyridine, and quinolone.